Heretofore, it has been recognized that to maintain substantially constant control pressure applied to a pressure regulator requires a complicated and expensive system. Various techniques have been employed to obtain the desired control all of which require the use of high cost, high precision components. One such prior system includes precisely controlling the input control pressure to a solenoid valve and the exhaust rate through an exhaust solenoid valve. This system requires continuous monitoring and pulsing of the solenoids for short periods of time until the desired pressure is achieved.
Due to the expense of precision solenoids and the precision control required to utilize lower cost solenoids, there has developed a need for control system that utilizes lower cost, less precise solenoids in a manner that does not require precision control. In accordance with the present invention, this goal is realized by a system using low cost solenoids in tandem with a buffer tank that acts as a pressure buffer. This system allows the low cost solenoids to act with the same effectiveness as high priced components.